Conventional humidifiers are typically constructed so that they atomize or vaporize water contained in a water reservoir either by means of an ultrasonic vibrating element (e.g. as shown in U.S. Pat. No. 4,238,425, the disclosure of which is expressly incorporated hereinto by reference) or by means of a heater. The thus atomized or vaporized water is then used to humidify the air in a room.
Water must always be resupplied to the reservoir to compensate for water removed therefrom in the form of vapor. Thus, it is important to maintain the water level in the reservoir above a preselected level since the ultrasonic vibrating element or the heater may become damaged should the water level in the reservoir fall below the preselected level.
Humidifiers have also been proposed, such as that shown in Japanese Laid Open Utility Model No. 53-13342, which stops the operation of an ultrasonic vibrating element and illuminates a neon light only in response to detecting whether the water level has fallen below the preselected level. As can be appreciated, no means are provided in the humidifier of Japanese Laid Open Utility Model No. 53-13342 which would permit one to readily determine whether the reservoir water level is at or above the preselected level (e.g. in a safe operating condition).